Type-1 diabetes (T1DM) is an autoimmune disorder which results in the selective destruction of more than 80% of endogenous insulin producing beta-cells (Pipeleers and Ling 1992). This disease most often appears during childhood or adolescence and is characterized by insulin deficiency, abrupt onset of symptoms, proneness to ketosis, and exogenous insulin dependency (Pociot and McDermott 2002). It is estimated that as many as three million people in the U.S. suffer from T1DM (Juvenile Diabetes Research Foundation, 2004).
Although exogenous insulin delivery has remained a suitable remedy for most T1DM patients, some individuals continually suffer from uncontrollable blood glucose-levels, leading to disease-related complications including blindness, neuropathy, nephropathy, myocardial infarction, stroke, and limb ischemia (Brownlee 2001). Over the last decade, islet transplantation has arisen as a potential alternative therapy for T1DM. Although islet-transplantation holds great promise, the scarcity of donor tissue makes such therapy available to <0.5% of potential transplant recipients.
A recent study has suggested that beta cells in the normal and regenerating adult murine pancreas are formed by self-duplication rather than contribution from a stem/progenitor cell (Dor et al. 2004). This data suggests a regenerative mechanism in the pancreas much like that described for the liver (Michalopoulos and DeFrances 1997). Under steady state conditions to moderate damage (damage ≦⅔ cellular mass), hepatocytes proliferate as a means to replace damaged cells (Michalopoulos and DeFrances 1997; Oh et al. 2002). It is not until this hepatic damage is followed by inhibition of hepatocyte proliferation (i.e., 2-AAF treatment), or severe loss of hepatocytes (90%), that a population of liver progenitor cells (termed oval cells) becomes activated and serves as a precursor for mature hepatocytes (Oh et al. 2002). Oval cells in the liver are bipotential progenitor cells, capable of giving rise to both hepatocytes and bile duct cells (Oh et al. 2002; Knight et al. 2005). Although not as extensively studied, oval cells have also been observed in the pancreas of rats and mice fed a copper-deficient diet (Ide et al. 1993; Jeffers et al. 1996). Phenotypically, mouse liver oval cells have been described as expressing numerous epithelial and hematopoietic markers including alpha fetoprotein (Afp), cMet, cytokeratins (CKs) 7, 8, 18, 19, CD34, CD45, Sca1, and Thy1 (Knight et al. 2005; Jeffers et al. 1996; Petersen et al. 2003; Petersen et al. 1998).
Cellular therapy with stem cells and their progeny is a promising medical treatment. Pancreatic islet transplantation provides a viable method for repopulation of pancreatic tissues damaged by disease or loss of pancreatic mass; however, current methods for culturing and maintenance of primary pancreatic culture are not sufficient for successful transplantation. Isolation and maintenance of pancreatic oval cells requires the addition of chemicals or other exogenous stressors (e.g., in vivo) for their proliferation making the cells less useful clinically (Jeffers et al. 1996; Petersen et al. 2003; Petersen et al. 1998; Wang et al. 2003; Rao and Reddy 1991). Therefore, a need exists to identify, isolate and characterize primitive cells that can differentiate into viable endodermal tissue, such as pancreatic tissue, and can be used in cellular replacement therapies, as well as to develop methods for isolating and culturing such cells without the need for the addition of chemicals or other exogenous stressors that may reduce the clinical applications of such cells.